In warehousing and upon the transport of goods, hand-driven forklifts and industrial trucks, which are also known as lift trucks or pedestrian trucks, are used. In order to reduce the physical stress of an operator or a warehouse worker, such vehicles are often equipped with motors for driving support and/or steering support. Based on the preferred use in closed buildings and the emissions behavior, electric motors are frequently used both for the operation and for steering, for example as drive motors and steering motors for the support of steering movements.
Traditional non-motorized supported industrial trucks usually feature a drawbar, which serves the purpose of specifying a steering direction or a driving direction by the operator.
While, for systems purely driven by motors, the drawbar solely serves the purpose of determining the driving direction and/or driving speed desired by the operator, industrial trucks and lift trucks also exist whereby the drive motors and steering motors have only a supporting effect such that a steering force or traction force and/or shear force applied by the operator is supported by the relevant motor. This requires, on the one hand, that such a force can be measured, for which a set of sensors on or in the drawbar has been established. On the other hand, this requires a mechanical connection of the drawbar with the rest of the drive, which can transfer both a traction force and/or shear force to the vehicle frame, and a steering force for steering a wheel of the drive around its steering axle. This is, in addition to a mechanical coupling of a steering motor with the steered wheel and/or the steered axle, a mechanical connection between the drawbar and the steered wheel and/or the steered component assembly is also necessary.
Drawbar-controlled industrial trucks without steering support are often driven with an electric drive unit, which can be pivoted around a vertical axis with the assistance of the drawbar. The drive may, for example, consist of an upright electric motor and a pivoting spur gear / bevel gear transmission, on the drive side of which a wheel or a running wheel, as the case may be, is mounted. These industrial trucks are steered by means of the force exerted by the operator on the drawbar, whereas the drawbar may be attached to, for example, the motor housing.
In the case of heavy industrial trucks, electrically controlled drive units are known for high loads and therefore high steering forces that arise on the drawbar. For steering that is purely operated by an electric motor, the drawbars are only used as transmitters or sensors, as the case may be, for guiding a steering movement.
There are also industrial trucks with electric steering support, with which the drawbar may be mechanically connected to the transmission, in order to transfer the steering movement of the drawbar directly to the transmission or a rotating component, as the case may be. Such industrial trucks frequently possess a turntable, in which a pinion of an electric steering motor engages, in order to support the steering movement and reduce the steering forces that an operator must apply. For industrial trucks with electric steering support, the drive motor or traction drive motor, as the case may be, is connected in a torque-proof manner with the vehicle frame, which requires a relatively complex design for the mechanical connection of the drawbar with the transmission of the drive motor. With some designs with steering support, the drawbar is rotatably mounted, for example, above the drive motor relative to the same, and a spur gear stage transfers the steering movement to a cardan shaft, which is guided at the traction drive motor and is connected to a gear, which, in addition to a pinion of the steering motor, engages in the turntable of the transmission. Such a complex control is intensive in terms of manufacturing costs, on the one hand, and maintenance, on the other hand, as, particularly in dirty environments of warehouses or the like, the moving parts of the shaft or the cardan shaft, as the case may be, must be lubricated on a regular basis. At the same time, such complex mechanical redirections can degrade the usability of such an industrial truck if, for example, the steering axle around which a wheel of the drive of the industrial truck rotates upon a steering movement is offset to the axis of the point of application of the drawbar, as, at that point, a haptic feedback or a feedback of the steering movement, as the case may be, can no longer satisfactorily reflect the actual steering angle of the wheel under certain circumstances, which can lead to faulty operation.
Thus, there is a need to make available a drive for an industrial truck that, with a provided support of a driving movement and at the same time a provided support of a steering movement, is more cost-effective and less maintenance-intensive than the previous drive.